The Framingham Study population is being utilized for studies on dementia in the elderly. The major focus will be on: (a) a search for risk factors for the development of dementia, (b) the clinical course of persons who appear to have been demented when examined 5 years previously, and (c) a search for early evidence of illness in persons who were not demented 5 years ago, but who have become demented in the interim. All study participants are currently receiving a brief mental status screening test as part of the regular (seventeenth biennial) examination. Participants suspected of intellectual impairment are being brought back for neurological and neuropsychological evaluation in order to identify individuals suffering from either SDAT or from MID. The analysis phase of this part of the study is expected to begin in 1984. In addition, an analysis of the prior neuropsychological test data has been undertaken by NIA and NHLBI staff. These prior results have been used to identify three groups to be the subjects of a followup study: the 212 persons who performed least well (the bottom 10 percent), 212 modal performers (25-75 the percentile range), and 170 of the top (greater than 75th percentile) performers.